UV curable coatings are one of the fastest growing sectors in the coatings industry. In recent years, UV technology has made inroads into a number of market segments like fiber optics, optical- and pressure-sensitive adhesives, automotive applications like UV cured topcoats, and UV curable powder coatings. The driving force of this development is mostly the quest for an increase in productivity of the coating and curing process. In various applications where minor and major repairs need to be performed swiftly and at ambient temperature on various substrates, UV technology promises to significantly increase the speed and integrity of repairs. Safety concerns associated with the use of UV lamps as well as economic constraints may likely preclude the use of high intensity light sources. Relatively inexpensive low intensity lamps that emit only in the UV-A region of the electromagnetic spectrum are taking their place, thus posing new challenges to resin developers and formulators.
UV curable coating compositions are known in the art. See, e.g., U.S. Pat. Nos. 4,188,472; 4,340,497; 6,465,539; and 6,534,128; and published PCT applications WO-97/04881 and WO-03/027162, each of which is incorporated by reference herein. In addition, U.S. Pat. No. 5,777,024 (incorporated by reference herein) is directed to the reaction product of a low viscosity isocyanurate group-containing polyisocyanate, which has been modified with allophanate groups to reduce its viscosity, with hydroxyl-functional olefinic compounds such as hydroxyalkyl (meth)acrylates and lactone modified versions of these (meth)acrylates. U.S. Pat. No. 6,306,504 (incorporated by reference herein) is directed to a coating composition for polycarbonate which contains the reaction product of a low viscosity polyisocyanate, such as a low viscosity isocyanurate group-containing polyisocyanate, with a hydroxy acrylate.
Various other UV curable coating compositions are also known in the art. See, in addition, U.S. Pat. Nos. 6,538,044; 7,294,656; and U.S. Patent Application Publication 2003/0059555, each of which is incorporated by reference herein.